Parameters

If hFile is a handle to a communications device, the function only flushes the transmit buffer.

If hFile is a handle to the server end of a named pipe, the function does not return until the client has read all buffered data from the pipe.

Return value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call
GetLastError.

The function fails if hFile is a handle to the console output. That is because the console output is not buffered. The function returns FALSE, and GetLastError returns ERROR_INVALID_HANDLE.

Remarks

Typically the
WriteFile and
WriteFileEx functions write data to an internal buffer that the operating system writes to a disk or communication pipe on a regular basis. The
FlushFileBuffers function writes all the buffered information for a specified file to the device or pipe.

Due to disk caching interactions within the system, the
FlushFileBuffers function can be inefficient when used after every write to a disk drive device when many writes are being performed separately. If an application is performing multiple writes to disk and also needs to ensure critical data is
written to persistent media, the application should use unbuffered I/O instead of frequently calling FlushFileBuffers. To open a file for unbuffered I/O, call the CreateFile function with the FILE_FLAG_NO_BUFFERING and FILE_FLAG_WRITE_THROUGH flags. This prevents the file contents from being cached and flushes the metadata to disk with each write. For more information, see CreateFile.

To flush all open files on a volume, call FlushFileBuffers with a handle to the volume. The caller must have administrative privileges. For more information, see
Running with Special Privileges.

When opening a volume with CreateFile, the lpFileName string should be the following form: \\.\x: or \\?\Volume{GUID}. Do not use a trailing backslash in the volume name, because that indicates the root directory of a drive.

In Windows 8 and Windows Server 2012, this function is supported by the following technologies.